Reinforced CMP carrier bladders

ABSTRACT

A reinforced bladder for a chemical-mechanical planarization (CMP) polishing device includes an elastomer infused with a reinforcing material. The elastomer can be a rubber such as EPDM. The reinforcing material can be a chopped fiber such as aramid. Alternatively, the reinforcing material can be a sheet (such as a triaxial or hexaxial weave of aramid) embedded in and infused with the elastomer.

FIELD OF THE INVENTION

[0001] The present invention relates to chemical-mechanical planarization (CMP) tools, and more particularly, to carriers for holding semiconductor wafers during polishing periods, and specifically to the bladders for use in carriers.

BACKGROUND

[0002] CMP tools are typically used to planarize the surface of a semiconductor wafer or to remove the upper portion of a layer formed on the semiconductor wafer (e.g., damascene processes). Some conventional CMP tools also include a rotating or non-rotating carrier to hold a wafer, and a rotating or orbiting platen or table with a polish pad. The CMP tool causes the polish pad and the wafer surface to come into contact, typically applying a specified pressure between the polish pad and the wafer surface. The CMP tool also imparts a relative motion between the wafer surface and the polish pad. Additionally, the CMP tool typically introduces a slurry at the interface between the polish pad and the wafer surface. The slurry can have abrasive particles suspended in a chemical solution that react with selected materials on the wafer surface. The pressure, slurry and relative motion effectuate the polishing.

[0003] This planarization or polishing is commonly accomplished by securing the wafer to a carrier, rotating the carrier and placing the rotating wafer in contact with a polishing pad mounted on a platen. A conventional wafer carrier typically includes a hard flat plate that does not conform to the surface of the wafer and is therefore covered by a softer carrier film that allows the hard plate to apply a more uniform polish pressure across the surface of the wafer. This process is known in the industry as back referencing technology. Back referencing is problematic in that in practice, it does not do a good job of providing uniform pressure on the wafer. In particular, when pressure is applied to the backside of the wafer, any inconsistencies between the backside of the wafer and the carrier film are translated to the front of the wafer by virtue of the direct contact involved.

[0004] In an effort to reduce the amount of non-uniformity caused by the back referencing technology, other systems use an inflatable bladder instead of the soft carrier film. The bladder allows for a two-way use of air. When a vacuum is applied and the bladder is in contact with the wafer, the carrier will pick up and hold the wafer in position. Next, the wafer is placed in contact with the polishing pad. Finally, the airflow is then reversed so as to provide a more uniform pressure between the wafer and the polish pad. This technique is known as front referencing technology.

[0005] Conventional bladders tend to bunch up or wrinkle during the polishing process. These wrinkles cause uneven local pressure to be applied directly to the wafer, which in turn is translated to the front side of the wafer to cause uneven polishing of the wafer. Additionally, the sidewalls of the bladder are subject to bowing and buckling during the polishing process, which contribute to the problem. Therefore, there is a need for a simple and inexpensive bladder that resists wrinkling, bowing and buckling compared to conventional bladders without a loss in axial movement (needed when vacuum and positive pressure are applied).

SUMMARY

[0006] In accordance with the aspects of the present invention, an improved bladder for use in a CMP tool is provided. In one embodiment of the present invention, the bladder is composed of an elastomer infused with a reinforcing material. In a further aspect, the elastomer is an ethylyne-propylene-diene monomer (EPDM) and the reinforcing material is an aramid fiber. In one embodiment, the aramid fiber is in the form of chopped fibers. The reinforcing material advantageously increases the fatigue, tensile strength and temperature tolerance performance of the bladder.

[0007] In another aspect of the invention, the bladder is formed with a woven fiber sheet. In one embodiment, the fiber sheet is formed using a triaxial/hexaxial weave where the sheet is infused in the elastomer during the processing phase while the rubber is still in a liquid state. This process allows the woven fabric to be embedded in and bonded with the elastomer as opposed to being laminated to the elastomer, resulting in similar advantages.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a diagram illustrating a CMP polishing tool with a back referencing bladder.

[0009]FIG. 2 is a cross-sectional view of the bladder and retaining ring.

[0010]FIG. 2A is a diagram of the bladder and retaining ring illustrating torque on the bladder surface.

[0011]FIG. 3 is a cross-sectional view of a bladder according to one embodiment of the present invention.

[0012]FIG. 4 is a more detailed view of a section of the bladder depicted in FIG. 3.

[0013]FIG. 5 is a cross-sectional view of a bladder according to another embodiment.

[0014]FIG. 6 is a diagram illustrating a view of the inside surface of the bottom of a bladder, according to one embodiment of the present invention.

[0015]FIG. 7 is a diagram illustrating a view of the inside surface of the bottom of a bladder according to another embodiment of the present invention.

DETAILED DESCRIPTION

[0016] The present invention represents a significant departure from conventional bladder technology employed in CMP tools by infusing reinforcing material into the elastomer used to form the bladders. This reinforcement provides, at a relatively low cost, a chemical-mechanical polishing bladder that reduces both wrinkling of the bladder face and buckle/bow of the bladder sidewall. In a further refinement, the reinforcing material is a chopped fiber, thereby facilitating the integration of the reinforcing material into the elastomer. In another embodiment, woven fabric is infused into the elastomer forming the bladder. This bladder technology is detailed below.

[0017]FIG. 1 illustrates a standard CMP tool with a carrier 14, platen 12, bladder 11, wafer 10, and a retaining ring 13, according to one embodiment of the present invention. In this embodiment, prior to polishing, a vacuum is applied between carrier 14 and bladder 11. The vacuum is then transferred to wafer 10 by way of the bladder 11 through perforations (not shown) in the bladder, which in turn causes wafer 10 to maintain contact with bladder 11. In another embodiment, selected areas of the bladder are molded to be thinner to allow the vacuum to be transferred to the wafer. Once the polishing process begins, the carrier 14 is moved so as to cause wafer 10 to come into contact with platen 12, which typically has a polishing pad mounted on its top surface. Positive air pressure is then applied between the carrier 14 and bladder 11 to inflate the bladder. The bladder provides uniform pressure to wafer 10, keeping the wafer in constant and uniform contact with platen 12.

[0018]FIG. 2 illustrates a cross-sectional view of the bladder 11 and its sidewall 22 component as well as retaining ring 13. During the operation of the CMP tool, pressure and torque are exerted on the bladder 11. When a vacuum is applied to the bladder, the bladder surface experiences an inward pressure. This inward pressure can cause a portion of the sidewall 22 to buckle in conventional bladders. When contact is made between the wafer 10/bladder 11 combination and platen 12 this excess rubber between the carrier 14 and platen 12 produces inconsistencies in the pressure applied to the wafer 10. However, as will be described below, a bladder according to the embodiments of the present invention has reinforcing material that reduces buckling. Similarly, when the bladder is inflated, the bladder surfaces experience an outward pressure. This outward pressure can cause a portion of the sidewall 22 to bow outward. This bowing stretches the bladder 11 and its sidewall 22, thereby undesirably reducing the useful life of bladder 11.

[0019]FIG. 2A illustrates the effect of torque τ on the bladder face 11 a. Bladder face 11A represents a three-dimensional extension of the bottom surface of the bladder 11. During operation both platen 12 and carrier 14 rotate to achieve optimal polishing. Torque τ occurs when wafer 10 contacts platen 12 and rotates. The bladder face 11 a experiences torque due to the friction caused by wafer 10 resisting rotation from platen 12. In conventional bladders, this leads to wrinkling of the bottom surface of the bladder face 11 a. Unfortunately, due to the close proximity of bladder face 11 a to wafer 10 and platen 12, the wrinkles cause an uneven buildup of rubber material along the back of the wafer. These uneven buildups of rubber material are then translated to the face of the wafer resulting in uneven polishing of the wafer. One design objective of this invention is to limit wrinkling, bowing, and buckling while allowing the bladder face 11 a to have enough axial movement to pick up and back-reference the wafer.

[0020]FIG. 3 illustrates a cross-sectional view of bladder 11 with reinforcing material, according to one embodiment of the present invention. The reinforcing material (e.g. see FIG. 4) is infused in the elastomer of the bladder. In one embodiment, the bladder is formed by adding the reinforcing material to an elastomer while the elastomer is still in a liquid state. The elastomer is then formed into a bladder using a standard injection molding process. Other embodiments could use any elastomer so long as its chemical properties are suitable for use in a CMP environment such as, for example, ethylyne-propylene-diene monomer (EPDM) or styrene butyl rubber (SBR) as well as other rubber materials.

[0021]FIG. 4 is a more detailed view of section 31 of bladder 11 (FIG. 3) and shows reinforcing material 41 infused in the elastomer of bladder 11. In this embodiment, reinforcing material 41 is a fiber material added during the injection molding process, as previously described. In this embodiment, the reinforcing material is chopped aramid fiber. Further, in this embodiment, the fibers are about 2 mm in length with a diameter of 20 mm, and are added to the elastomer to about 6% density by volume. In other embodiments, the fiber length can range from 1 mm to 10 mm, with diameters ranging from 20 mm to 50 mm, and density ranging from 3 to 10%, depending on the size and application of the bladder, the reinforcing material, etc. In a still further embodiment, chopped KEVLAR® fiber is used. Although FIG. 4 shows the reinforcing material 41 as being visible, in actual use, reinforcing material 41 is not visible when the 2 mm 6% density chopped KEVLAR® is used. When the fiber density exceeds 10% the fiber in the bladder can be visible to the naked eye, which may be undesirable in some applications. Other embodiments could use other fibers including any from the class of polyesters, or wool, cotton, or even glass fibers. In general, multifilament spun fiber as well as para-aramid fiber fabrics can be used so long as their properties meet the requirements for use in a CMP tool.

[0022]FIG. 5 illustrates another embodiment of the present invention. This embodiment uses a fiber sheet 51 embedded in the face of the bladder for reinforcement. The sheet reinforcement 51 can be made of any suitable fiber listed above or of any fiber whose properties would be suitable enough for use in a CMP tool. In one embodiment, fiber sheet 51 is a fiber sheet formed using a triaxial/hexaxial weave. The sheet is infused with the elastomer during the processing phase while the rubber is still in a liquid state. The triaxial/hexaxial weave of this embodiment of fiber sheet 51 provides essential isotropic reinforcement of the bladder face against wrinkling.

[0023]FIG. 6 is a diagram illustrating a view of the inside surface of the bottom of a bladder, according to one embodiment of the present invention and describes bladder 11 including sidewall 22 and bladder face 11 a.

[0024]FIG. 7 is another embodiment of the invention illustrating a multi-zone carrier bladder. FIG. 7 is similar to FIG. 6 with the exception of an additional sidewall 72 that is used to define another zone in the bladder. During the polishing process the annular zone outside of sidewall 72 can have a different pressure than the circular zone inside of sidewall 72. The pressures within these zones may be varied as needed to achieve a desired removal rate profile for a particular polishing application. Other embodiments may have more than one sidewall, with four to five zones being common.

[0025] Although the description above refers to wafers, other embodiments of the present invention can be adapted for other types of workpieces. For example, a workpiece may be semiconductor wafer, a bare silicon or other semiconductor substrate with or without active devices or circuitry, a partially processed wafer, a silicon or insulator structure, a hybrid assembly, a flat panel display, a micro electromechanical structure (MEMS), a disk for a hard drive memory, or any other material that would benefit from cleaning or planarization.

[0026] The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended. 

We claim:
 1. A bladder for use in a carrier of a CMP tool, comprising an elastomer infused with a reinforcing material, wherein the reinforcing material increases the rigidity of the bladder.
 2. The bladder of claim 1 wherein the elastomer comprises an ethylyne-propolyne-diene monomer compound.
 3. The bladder of claim 1 wherein the reinforcing material comprises a plurality of fibers.
 4. The bladder of claim 3 wherein the plurality of fibers includes multifilament spun fiber.
 5. The bladder of claim 3 wherein the plurality of fibers comprises woven fibers.
 6. The bladder of claim 3 wherein the plurality of fibers comprises chopped aramid fiber.
 7. A bladder for use in a carrier of a chemical-mechanical planarization (CMP) tool, comprising: an elastomer shaped to form the bladder; and a sheet of reinforcing material, wherein the sheet of reinforcing material is embedded in and infused with elastomer.
 8. The bladder of claim 7 wherein the elastomer comprises an ethylyne-propolyne-diene monomer compound.
 9. The bladder of claim 7 wherein the sheet of reinforcing material comprises aramid fiber.
 10. The bladder of claim 7 wherein the sheet of reinforcing material comprises a triaxial weave of fiber.
 11. The bladder of claim 7 wherein the sheet of reinforcing material comprises a hexaxial weave of fiber.
 12. A bladder for use in a CMP tool, comprising: an elastomer shaped in the form of a bladder; and means, infused in the elastomer, for reinforcing the elastomer, wherein the bladder has increased rigidity.
 13. The bladder of claim 12 wherein the means for reinforcing comprises a plurality of fibers.
 14. The bladder of claim 13 wherein the plurality of fibers comprises chopped fiber.
 15. The bladder of claim 12 wherein the means for reinforcing comprises a sheet of reinforcing material.
 16. The bladder of claim 15 wherein the sheet comp rises woven aramid.
 17. A method for polishing a workpiece using a CMP tool, the method comprising: loading the workpiece in the CMP tool; polishing the workpiece using the CMP tool, wherein the CMP tool includes a reinforced bladder, wherein the reinforced bladder comprises an elastomer infused with a reinforcing material.
 18. The method of claim 17, wherein the reinforcing material comprises a plurality of fibers.
 19. The method of claim 18, wherein the plurality of fibers includes multifilament spun fiber.
 20. The method of claim 18, wherein the plurality of fibers comprises chopped aramid fiber.
 21. The method of claim 17, wherein the reinforcing material comprises a sheet of reinforcing material.
 22. The method of claim 21, wherein the sheet of reinforcing material comprises aramid fiber.
 23. A CMP tool for polishing a workpiece, comprising: means for loading the workpiece; means for polishing the workpiece, the means for polishing including a bladder, wherein the bladder comprises an elastomer infused with a reinforcing material. 